Effects of brazilin on the phospholipase A(2) activity and changes of intracellular free calcium concentration in rat platelets

Brazilin {7,11b-dihydrobenz[b]indeno[1,2-d]pyran-3,6a,9,10(6H)-tetrol} inhi bited thrombin-, collagen- and ADP-induced aggregation of washed rat platel ets. Thrombin- and collagen-induced ATP release were also inhibited by braz ilin in a concentration-dependent manner. Brazilin inhibited the formation of platelet thromboxane A(2) caused by thrombin, whereas it had no effect o n the prostaglandin D-2 formation. Brazilin inhibited [H-3]-arachidonic aci d liberation from membrane phospholipids of thrombin-stimulated platelets. Brazilin inhibited the rise of intracellular free calcium caused by thrombi n. These results indicate that the inhibition of phospholipase (PLA(2)) act ivity and [Ca2+](i) elevation might be at least a part of antiplatelet mech anism of brazilin.